Production of artificial filaments



PRODUCTION OF ARTIFICIAL FILAMENTS W. l. TAYLOR Filed Dec. 8, 1950 I F/ ///72 27 I5 3O i E: I

2,7 66,099 PRODUCTIQN F ARTIFICIAL FELAMENTS William Ivan Taylor, Spondon, near Derby, England, assigner to British Celanese Limited, a corporation of Great Britain Application December 8, 1950, Serial No. 199,733

Claims priority, application Great Britain December 22, 1945 Claims. (Cl. 8-131) This invention relates to the production of artificial filaments and is particularly concerned with a method and apparatus for the production of continuous filaments of large cross-section from a number of finer fibres.

According to the present invention a method for the production of a continuous filament of large cross-section comprises passing a thread of fibres each of finer crosssection upwards in a straight line into and through a body of solvent liquid for the substance of at least some of said fibres, and causing said thread to continue substantially in a straight line beyond said body of liquid until it is set by the drying of the solvent liquid picked up by it. In this way, lateral pressure on the thread liable to cause flattening thereof which is reproduced as a permanent feature of the resulting unitary filament can be avoided, since the thread is not substantially deflected from a straight course either where it goes into and through the body of solvent liquid (the most critical stage) or where it is in a soft and plastic condition thereafter. Moreover, the solvent liquid is applied in a manner which is symmetrical about the thread and uniform along its length.

The body of solvent liquid is contained in a vessel having a hole therein below the level of the liquid in the vessel and of a size suitable for the easy passage of the thread upwards into the vessel, and the invention includes an apparatus comprising such a vessel, together with guide means above and below said hole and in alignment therewith, and means for drawing a thread upwards through said guide means and said vessel. The size of the hole is not critical; it may be somewhat larger than the cross-section of the thread provided that the speed of passage of the thread is suificient to prevent the solvent liquid flowing away through the hole.

The invention is particularly applicable to the production from a thread of fine continuous filaments of a heavy filament of round cross-section, a result which it is difficult to attain if the cross-section is disturbed by lateral pressure before the product is set. In this case it is desirable that the continuous filament thread should possess some degree of twist, e. g. of the order of 3 to 6 turns per inch, which twist is sufiicient, in the absence of lateral pressure, to give the thread a round cross-section which is reproduced in the product. If the thread consists of or contains staple fibres instead of or in addition to the continuous filaments, some degree of twist is desirable also to give coherence to the thread.

In order to control the amount of solvent retained by the thread after passing through the solvent, it may be convenient to cause the thread to pass through a stripping die disposed a short distance above the surface of the body of solvent, and such a stripping die can be so shaped as to modify the cross-section and to produce a 2,756,99 Patented Get. 9, 1956 unitary filament of a cross-section that is not round. The stripping die should be carefully aligned so as not to deflect the thread from its straight course, and should be close enough to the surface of the solvent to prevent the accumulation of deposits of the substance of the filaments beneath the die, which would tend to obstruct the die. Where a round product is desired, however, the stripping die can be dispensed with, and the amount of solvent picked up by the thread can be controlled by controlling the depth of solvent liquid through which the thread passes.

The drying of the product during its upward passage from the vessel can be effected in free air, or it can be carried out in an enclosed passage or tube of suitable length along which the product passes and to which suction is applied so as to draw a current of evaporative medium, conveniently air, along the tube to remove solvent-laden air from the vicinity of the product. Such solvent-laden air can be conducted to a suitable plant for the recovery of solvent therefrom. The tube may be heated so as to encourage the drying of the product.

The invention is particularly applicable to the production of continuous filaments of large cross-section having a basis of cellulose acetate or other organic derivative of cellulose. Examples of other cellulose derivatives which may form the basis of the filaments are other esters and mixed esters of cellulose such as cellulose propionate, cellulose acetate-propionate and cellulose acetate-butyrate, and cellulose ethers such as ethyl cellulose. As the solvent, any liquid can be used that exerts a sufiicient softening action on the substance of the thread for its individual fibres to coalesce into a unitary product, and that is sufficiently volatile for the product to set by drying. Examples of solvents suitable for use with cellulose acetate are acetone (commercially pure or mixed with Water), triacetin, ethyl lactate, diacetone alcohol and mixtures of diacetone alcohol with water or alcohol. The solvent liquid may also contain dyes or other effect materials for application to the thread simultaneously with the solvent. Moreover the thread may have a content of fibres, whether staple fibres or continuous filaments, of a substance which is not softened by the solvent liquid employed, such fibres being bound into the product by the coalescence of a content of fibres which are so softened.

By way of example, two forms of apparatus in accordance with the invention, and methods of producing heavy filaments of round cross-section by means of the apparatus, will now be described in greater detail with reference to the accompanying drawings in which,

Figure 1 is a diagrammatic side elevation of one form of apparatus,

Figure 2 shows a detail of Figure l on an enlarged scale,

Figure 3 shows, in diagrammatic side elevation, a modification of a part of the apparatus shown in Figure l and,

Figure 4 is a sectional plan of the modification shown in Figure 3.

Referring to Figures 1 and 2, a reel or bobbin 5 constitutes a source of supply from which is drawn a thread 6 made of continuous filaments of cellulose acetate. The thread 6 is one formed from a plurality of finer threads, each of 300 denier and consisting of 52 filaments twisted together with 2.5 turns per inch 8 twist, the finer threads being doubled in pairs with 2.5 turns per inch Z twist, and 7 ends of the 2-fold thread being cabled together with 5 turns per inch 8 twist to form the thread 6, which is thus a cabled thread of approximately 4200 denier. The

cabled thread 6 is drawn from the bobbin at a speed of about 25 metres per minute and passes upwards, by way of a rotating V pulley 7 serving as a thread guide, through a die hole 8 of 0.032" diameter. The die hole 3 has a rounded entrance and is formed in the floor of a troughlike vessel 9, 2" deep, containing acetone to a depth of 1". A continuous flow of acetone is fed to the trough 9 by way of a supply pipe 10, the pipe 10 communicating with a reservoir 11 of acetone through a control valve 12. An over-flow pipe 13 projects upwards through the bottom of the trough 9 to a height of l and leads the excess supply of acetone to a waste reservoir 14.

The thread 6 passes upwards from the surface of the liquid in the trough 9 and through a stripper die 15, also of 0.032" diameter, formed in a die plate 16. The plate 16 is secured by wing nuts 17 to a stand 18, the two dies 8, being carefully aligned with the bottom of the groove in the guide pulley 7 so that the thread is not deflected by the die 8. The stripper die 15 may be dis posed at about 4" above the bottom of the trough 9. This height may be adjusted by means of the nuts 17 to suit the conditions obtaining but should not, for the speed mentioned, exceed about 8" since above this height dope tends to accumulate beneath the die plate 16.

From the die 15 the thread 6 passes upwards through a distance of about 4 metres in free air, in the course of which evaporation of the acetone from the product takes place. The resulting unitary product 19 passes through a further guide 20, substantially in alignment with the two dies 8, 15 and with the guide pulley 7 but adapted to be traversed over a short distance so as to distribute the product 19 on the surface of a take-up swift 21. The swift 21 is driven by means of sprockets 22 and chains 23, by way of a clutch 24 enabling the swift to be started and stopped. The rotation of the swift draws the thread 6 and the resulting unitary product 19 from the supply reel or bobbin 5 and through the apparatus. With a winding speed of 25 metres per minute and a drying run of 4 metres, as stated above, a room temperature of about 22 C. is enough for the product to dry sufiiciently to prevent sticking thereof on the swift.

The product 19 is a unitary filament of good round cross-section having a diameter of 0.03" which is maintained along the length of the product within close limits. If a coloured product is desired, an acetone soluble dyestuff can be employed, dissolved in the acetone in the trough 9. Thus, for example, if a deep green colour is desired the acetone may contain 1.0 gramme/litre of Xylene Fast Green B (Colour Index No. 735) or, if a deep red is desired, the acetone may contain 1.5 grammes/litre of the azo dye formed by coupling diazotised paranitroaniline with metastearylamino-diethylaniline.

Instead of drying the product in free air as described with reference to Figure 1 it may, as shown in Figures 3 and 4, be caused to pass along a tube 26, 10" in length and 4" in diameter. The upper end of the tube 26 is closed except for a guide hole 30 affording a good clearance for the product and guiding the product to the traversing guide leading to the collecting swift. The tube 26 is provided with a lateral suction pipe 27 through which solvent-laden air is drawn oif and led to a solvent recovery plant. Surrounding the tube 26 is a jacket 28 containing four lengths 29 of /2" steam pipe connected in series and each extending along the length of the jacket 28. By supplying steam through the pipes 29, the tube 26 is heated. As shown in Figure 3, the stripper die can be dispensed with (whether the heated tube 26 is employed or not) and the amount of acetone picked up by the thread 6 can be controlled by varying the height of the over-flow pipe 13 above the bottom of the trough so as to vary the depth of acetone maintained in the trough. Since it is important to guide the thread 6 straight through the die hole 8 it is desirable, when the stripper plate 16 is omitted, to provide a further guide for the product before the product reaches the traversing guide 20. The further guide is disposed in line with guide pulley 7 and the die hole 3. In Figure 3 the clearance hole 30 at the top of the tube 26 serves this purpose.

The size of the hole 8 in the floor of the trough 9 by which the thread 6 enters the trough is not critical; it may be substantially larger than the diameter of the thread, provided that the speed of passage of the thread is sufiicient to prevent the acetone in the trough 9 flowing away through the hole 8. In starting the operation, the thread 6 is led from the supply package and through the apparatus to the collecting reel 21, and the clutch 24 is engaged so as to start the reel before acetone is supplied to the trough 9.

Having described my invention, what i desire to secure by Letters Patent is:

1. A method of producing a continuous unitary filament of large cross-section, said method comprising passing a thread of artificial thermoplastic fibres vertically upwardly in a straight line freely into and through a hole in the bottom of a vessel containing a body of a liquid which is a solvent for the substance of at least some of said fibres and then passing said thread freely vertically in said straight line through said body of liquid, said hole being larger than the cross-section of said thread, and causing said thread to continue substantially in a straight line beyond said body of liquid until it is set by the drying of the solvent liquid picked up by it, the speed of passage of said thread through said hole being sufiiciently high, taken in conjunction with the size of said hole, to prevent said liquid from escaping downwards through said hole, and the speed of passage of said thread through said body of liquid being sufficiently high, taken in conjunc' tion with the depth of said body of liquid, that the integrity of said thread is maintained while individual artiticial thermoplastic fibres of said thread are softened by the action of said liquid and coalesced.

2. The method of claim 1 wherein the thread consists of a plurality of fine continuous filaments.

3. The method of claim 2 wherein the thread which is passed upwardly through said body of liquid is a twisted thread and the product of the process has a round crosssection.

4. The method of claim 1 comprising stripping excess solvent liquid from the thread after it has emerged from the body of solvent liquid and in the course of its straightline passage.

5. The method of claim 1 comprising passing the thread through a current of heated evaporative medium to accelerate evaporation of the solvent liquid and in the course of its straight-line passage.

6. The method of claim I wherein the thread contains fibres of cellulose acetate and wherein the solvent liquid is acetone.

7. The method of claim 1 comprising incorporating in the solvent liquid an effect material adapted to be retained by the thread after drying of the solvent liquid.

8. The method of claim 7 wherein the effect material is a dyestuff for the substance of the fibers.

9. A method of producing a continuous unitary cellulose acetate filament of large, round cross-section, said method comprising passing a twisted thread of continuous filaments of cellulose acetate vertically upwardly in a straight line freely into and through a hole in the bottom of a vessel containing a body of acetone and then passing said thread freely vertically in said straight line through said body of acetone, said hole being larger than the cross-section of said thread, causing said thread to continue substantially in a straight line beyond said body of acetone and, in the course of said straight line passage, stripping excess acetone from said thread after it has emerged from said body of acetone and passing said thread through a current of heated evaporative medium so as to set the thread by the drying of the acetone picked up by it, the speed of passage of said thread through said hole being sufiiciently high, taken in conjunction with the size of the hole, to prevent said liquid from escaping downwards through said hole, and the speed of passage of said thread through said body of liquid being sufllciently high, taken in conjunction with the depth of said body of liquid, that the integrity of said thread is maintained While individual cellulose acetate filaments of said thread are softened and coalesced.

10. The method of claim 9 comprising dissolving in the body of acetone a dyestufi? for cellulose acetate.

References Cited in the file of this patent UNITED STATES PATENTS Taylor May 16, 1933 Taylor Nov. 7, 1933 Dreyfus Sept. 22, 1936 Galatioto July 15, 1941 Hukle Aug. 4, 1942 Oberly Jan. 29, 1952 FOREIGN PATENTS Great Britain Apr. 12, 1937 

1. A METHOD OF PRODUCING A CONTINUOUS UNITARY FILAMENT OF LARGE CROSS-SECTION, SAID METHOD COMPRISING PASSING A THREAD OF ARTIFICIAL THERMOPLASTIC FIBRES VERTICALLY UPWARDLY IN A STRAIGHT LINE FREELY INTO AND THROUGH A HOLE IN THE BOTTOM OF A VESSEL CONTAINING A BODY OF A LIQUID WHICH IS A SOLVENT FOR THE SUBSTANCE OF AT LEAST SOME OF SAID FIBRES AND THEN PASSING SAID THREAD FREELY VERTICALLY IN SAID STRAIGHT LINE THROUGH SAID BODY OF LIQUID, SAID HOLE BEING LARGER THAN THE CROSS-SECTION OF SAID THREAD, AND CAUSING SAID THREAD TO CONTINUE SUBSTANTIALLY IN A STRAIGHT LINE BEYOND SAID BODY OF LIQUID UNTIL IT IS SET BY THE DRY- 